sleder

I have a '90 C2. H&R cup suspension, rolled fenders and need to get another set of wheels. I am currenly running Cup's 7 & 9's. I want as much rubber as is smart for a stock R&P and gears. I am looking for advise whether to go 17's or 18's. BTW the use is Club Racing. most frequently used tracks are WG, VIR, SP...
TIA
If you have something for sale in this regard so be it, let me know.

Greg Fishman

Go with 18's. They will be faster, notice the top cars in your class will be on 18's too.

sleder

With a stock gear set and R&P will the 18's give me the feeling of being slower to pull away out of a corner?

JackOlsen

17 versus 18 doesn't matter. It's the outside diameter of the tires you're using that will make a difference, and there's no correlation between that and rim size. Decide on what tire sizes you'd want to run, and look at the difference between outside diamters of those tires. With some tire sizes, it's possible to run a smaller total diameter on a larger diameter wheel.

Can you run 8's and 10's in your class? Assuming you can, then start by looking at the available 245 and 275 tires in both 17 and 18. For example, a 245/45x17 tire has an outside diameter of 25.7 inches. A 245/35x18 is a full inch smaller (24.7) in diameter. To get the same total diameter in a 245, you'd have to run a 245/40x18.

In Hoosier's 245 width, the two available overall diameters of the tires are 24.7 and 25.7. This is true in both 17-inch and 18-inch sizes. There is no 18-inch size that would offer a larger diameter than the 17-inch wheel, so there'd be no effective change in gearing (although you'll pay $36 more for the 18-inch tire).

The other handling factors will be sidewall rigidity (which will generally correspond to sidewall height) and weight -- although again with weight, the results can be counterintuitive, since when you get to very lightweight wheels, the larger-diameter wheel/tire package can often weigh less than the smaller wheel with the bigger tire (again with the two wheel/tire combos producing the same overall tire diameter).

Does that make sense?

Greg Fishman

What Jack said. The overall circumference or diamater is what will matter as far as acceleration. A taller tire will turn few rpm and may decrease acceleration, but it may help you at certain tracks where you are inbetween gears. You need to run 8.5 and 10 or 10.5 rims to get the right rubber under your car. 245/275 or 285 is what most guys with 964's run.
I have done back to back testing with 17 and 18's and even if you gave up a small amount of acceleration (don't think you will) the cornering speed and stability more than makes up for it.

sleder

This is a great lesson to be learned prior to spending all the money on wheels and tires. I didn't think I could stuff a 285 under it...I knew it would handle the 245 and 275 combination. If I go to 18's what sizes would you recommend?
Thank you both for the information and help. I want to do this right the first time I purchse these...

Greg Fishman

You are welcome, glad to help. I can't guarantee you that a 285 will work, and even if it did you may want to stay with the 275, there seems to be some issues with the 285 on rear engine cars as that tire has a very low air volume. Either way the wheel size for a 275 or a 285 are the same, so you can always test fit and see which you like better.

My suggestion on wheels is to call David Schardt at www.forgeline.com he is a club racer and owns Forgeline wheels. Very nice wheels at a reasonable price and he can custom make them for your particular car.

sleder

Greg I have corresponded with Mark Schetter, however I have recently been told of cracking issues and thought perhaps I should spend more up front and get less problems later. Forgeline is closing out their 2 pce wheels and will only be making the 3 pce in the future. Great pricing on the 2 pce. Though isn't not only about price.

Greg Fishman

I have not heard about any issues with the 3 piece wheels, and I know a fair number of people that own them. I am pretty sure the 2 piece wheels weren't made in 18's, only 17's and I have heard of a few people having issues with those but it was more with leaks than cracks.

I have owned BBS, and Kinesis and they are both good wheels but nothing is immune from issues and they are a wear item that needs to be checked often and replaced over time.